The present invention relates to a vehicle having an automatic transmission and an automatic engine start and stop system.
Modern vehicles with internal combustion engines are increasingly being equipped with a so-called automatic engine start and stop system. In such start and stop systems, a complex electronic control and/or regulating unit operates to switch off the internal combustion engine during “travel interruptions,” such as while being stopped at traffic lights, and to automatically restart the internal combustion engine, when the driver gives a “restart signal.” Such engine start and stop systems were initially introduced in vehicles with a manual transmission. In vehicles with manual transmissions, the engine is switched off when the vehicle stops moving, as soon as the transmission is shifted into a neutral or idle mode and certain boundary conditions (engine oil temperature, outside temperature, etc.) are fulfilled. The internal combustion engine is automatically restarted by stepping on the clutch pedal.
Vehicles with an automatic transmission have a variety of transmission shift elements (clutches, brakes, etc.) that are actuated by an electrohydraulic system. A condition for actuation is that the oil pressure must be adequately high. When a vehicle with an automatic transmission and a transmission oil pump, which is mechanically driven by the internal combustion engine, is started, it may take less than a second for the oil pump to build up enough oil pressure for gear shifting and, in so doing, to drive off. However, in vehicles with an automatic transmission and an automatic engine start and stop system, the delay time to build up the oil pressure required to drive off after starting the internal combustion engine must be as small possible, because in the “stop and go mode” the standard startup delay time of several tenths of a second would not be accepted by customers.
The object of the present invention is to provide a vehicle that has an internal combustion engine, an automatic transmission and an automatic engine start and stop system, wherein an engine start and stop mode enables as small a startup delay as possible after starting the internal combustion engine.
This and other objects are achieved by a vehicle equipped with an internal combustion engine, an automatic transmission, which has an electrohydraulic transmission control unit, a transmission oil pump, which is driven directly or indirectly by the internal combustion engine, and an electronic engine start and stop system, which switches off the internal combustion engine in operating phases, in which the vehicle is temporarily stopped, if predefined operating parameters are present, and starts the internal combustion engine if a restart signal is present. A purely mechanical pressure accumulator device provides stored hydraulic pressure, or more particularly the stored hydraulic fluid, to the electrohydraulic transmission control unit in a time period following the starting of the internal combustion engine, in which the transmission oil pump is still building up pressure.
The starting point of the invention is a vehicle with an internal combustion engine and an automatic transmission, which has an electrohydraulic transmission control unit. The transmission shift elements, such as clutches or brakes, are hydraulically actuated by the electrohydraulic transmission control unit. The hydraulic pressure required for this purpose is supplied by a transmission oil pump that is mechanically driven by the internal combustion engine. The transmission oil pump can be mechanically driven directly or indirectly by the internal combustion engine. The transmission oil pump can be mounted, for example, on a transmission input shaft of the automatic transmission. The transmission oil pump can be, for example, a gear pump or a rotary vane pump.
Furthermore, the vehicle has an electronic engine start and stop system, which “automatically” switches off the internal combustion engine in operating phases, in which the vehicle is temporarily stopped, such as in “stop and go mode,” at a red light etc., if predefined operating parameters are present. The start and stop system automatically starts the internal combustion engine if a “restart signal” that is predefined by the driver is present.
According to an aspect of the invention, a purely mechanical pressure or more particularly a volume accumulator device intended for storing hydraulic fluid provides the stored hydraulic pressure, or rather the stored hydraulic fluid, to the electrohydraulic transmission control unit in a time period following the restarting of the internal combustion engine, in which the transmission oil pump is still building-up pressure.
It is important that the “triggering” or rather the emptying of the pressure accumulator device or, more specifically, the volume accumulator device, after restarting the internal combustion engine occurs by purely mechanical measures and/or purely hydraulic measures alone—that is, without electrically actuated components. In this context “triggering” means “switching over” the pressure accumulator device or rather the volume accumulator device from one state, in which it stores the hydraulic fluid, into a state, in which it pushes the stored hydraulic fluid into the hydraulic system of the transmission control unit and, in so doing, moves this transmission control unit directly into a ready-to-run state.
The signal that is necessary for triggering is formed by the buildup of pressure that is generated by the transmission oil pump driven by the internal combustion engine.
On the whole, the “loading,” the “pressure storage” and the “discharging” of the pressure accumulator device, or more specifically the volume accumulator device, occur by purely mechanical devices or, more specifically, by purely hydromechanical/hydraulic devices alone—that is, without any electrical and/or electronic control or regulating unit and without any electrical and/or electronic components.
This approach has the advantage of achieving with a simple and cost effective design that the transmission shift operations that are required for startup can be carried out with nearly zero delay directly after starting the internal combustion engine. Therefore, in contrast to conventional vehicles with automation transmissions, it is possible to produce a significantly faster “startup readiness.”
According to a further aspect of the invention, the pressure accumulator device has an accumulator cylinder with an accumulator piston, which is arranged in a displaceable manner in the accumulator cylinder. This accumulator piston is prestressed by way of a spring in a direction, in which pressure is applied, and can be locked in a tensioned state by a purely mechanical locking device. If the internal combustion engine is switched off and then restarted again, it is only required that the locking device be released, in order to convert the spring energy, stored in the spring, into hydraulic pressure and, in so doing, to bridge the time period until the transmission oil pump has reached its normal operating pressure.
The locking device can be formed by a locking piston that interacts with the accumulator piston and that is arranged in a displaceable manner in a locking cylinder. The locking piston can be provided with a locking pin, which can engage with a recess of a piston rod of the accumulator piston. In the engaged state the locking device locks. The locking piston can be prestressed by use of a locking spring in the direction of its locking position.
According to a further aspect of the invention, the locking piston has a passage borehole that acts as an orifice. The locking cylinder is divided by the locking piston into first and second locking cylinder chambers, and the first and second locking cylinder chambers are in fluid communication with each other by way of the passage borehole.
The first locking cylinder chamber can be in direct fluid communication with a pressure output of the transmission oil pump. Furthermore, the pressure output of the transmission oil pump can be in fluid communication with the second locking cylinder chamber and the electrohydraulic transmission control unit by way of a check valve. The check valve is arranged such that it can be opened by way of the hydraulic pressure of the transmission oil pump (and locked in the reverse direction of pressure).
It is especially important that the locking spring builds up enough static pressure that the locking piston is actuated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.